This invention relates generally to equipment for attaching adjacent pieces of carpet together to form a secure seam which will withstand stretching. More particularly, the invention is concerned with a seaming iron and hot melt carpet seaming tape, wherein the iron is tracked over the tape and between the adjacent carpet edges so that adhesive on the tape is melted and the seam made as the iron progresses forward.
Hot melt carpet seaming tape and irons for use with the tape are well known. For example, see U.S. Pat. Nos. 4,536,244, 4,714,514, 3,748,211, 3,927,298, 3,523,176 and 3,400,245.
In the 1960s, carpet seaming tape largely replaced seam stitching as a means of joining two pieces of carpet together for a stretched carpet installation. The use of the hot melt carpet seaming tape, applied to the carpet backings while the carpet lies in the finished, face up position, has been far more efficient than seam stitching.
However, a problem with carpet seaming tape has been that it exhibits seam peaking when stretched. Tension across the seam is accepted by the tape, through its width, with the carpet above not encountering as much tension as the tape. The carpet seaming tape has a thickness which is apparently sufficient to contribute to the problem of peaking, by raising the line of tension somewhat at the joint, thereby tending to raise the tape to the mid-level of the carpet backing in the surrounding areas of the carpet. The causes of seam peaking have to do with the relatively thick carpet backings being held together only along the plane of their bottom surfaces. The carpet pile protrudes upwardly at the joint, forming a small peak at the seam line.
The causes of seam peaking have not always been completely understood. For example, one attempt to alleviate this problem was to increase the width of the carpet seaming tape and of the hot melt adhesive on the tape, from about three inches to about six inches. See Johnston et al. U.S. Pat. Nos. 4,749,433 and 4,919,743. This was only effective to spread out the rise of the carpet over a wider area, with seam peaking still occurring and being very noticeable at the seam line between the carpet pieces. As explained below, the present invention takes the opposite approach, by providing a far narrower band of hot melt adhesive on a carpet seaming tape.
It has been recognized previously that a carpet seam can be made with greater integrity if a portion of the hot melt adhesive is applied against the edges of the carpet backing, to form a butt seam or welded seam wherein the actual edges of the carpet backing are strongly bonded together, in addition to the connection made by adhesion of the tape to the bottom side of both pieces of carpet on either side of the joint. For example, the above referenced U.S. Pat. No. 4,536,244 discloses an iron base plate having a deep center groove and a chevron formation for gathering melted adhesive in a raised center bead formed on the tape as the seam is being made with the iron. The object of the raised center bead was to cause molten adhesive to be applied to the side edges of the backings as those backings were lowered onto the tape behind the iron.
U.S. Pat. No. 4,535,244 also mentioned that carpet manufacturers have suggested the installer should manually apply liquid solvent or water based (latex) adhesive to the backing edges, before hot melt seaming. However, any latex adhesive applied to areas where hot melt is to be received will reduce the bond strength of the hot melt adhesive.
A manual tool for applying liquid (not hot melt) adhesive to side edges of linoleum and carpet backings was disclosed in Despins U.S. Pat. No. 4,484,976.
In addition, U.S. Pat. No. 4,536,244 made a brief reference that the carpet seaming tape used in conjunction with the seam welding technique could be made narrower for reasons of economy, due to the added strength afforded by the strong butt welded joint between the carpet backings. However, the patent did not suggest the structure of the carpet seaming tape of the present invention, nor did the patent recognize or suggest that a narrow strip of adhesive on a carpet seaming tape, in conjunction with seam welding wherein the edges of the carpet backings are butt-joined, can provide the benefit of reducing and nearly eliminating seam peaking in a stretched carpet installation.
In accordance with the present invention described below, it has been discovered that the edge bonding of the carpet backings at the seam, particularly when accompanied by the use of a very narrow tape not contemplated for this purpose in the prior art, provides a strong seam which will exhibit little or no seam peaking. A seaming iron, narrow-adhesive band type and a method of installation are provided for this purpose.